I. Field of the Invention
The present invention relates to continuous pour, high temperature electronic furnaces suitable for converting large volumes of fly ash into high quality mineral wool, apparatus used in connection with such furnaces, the resultant mineral wool products, and methods for manufacturing those products.
II. Description of the Prior Art
The production of electrical power from coal using standard combustion methods leaves coal fly ash as a by-product. This fly ash is a health and environmental hazard, and presently is an economic liability to an electrical power producer.
Mineral wool is a fine fibrous "wool-like" material, typically made by deflecting a small stream of molten rock or similar material, such as fly ash, with a jet or stream of fluid, or with a rotating wheel of a spinner. The action of the jet of fluid, or spinner, deflects the mineral wool into fibrous strains which harden before the strains reach the floor. Balls of hardened material which do not deflect into fibrous strands called "shot" are also formed, either attached or unattached to the strains. Accumulated, the fibrous strands form mineral wool which has great utility as temperature and sound insulation.
A manufacturing process of converting fly ash into mineral wool ideally requires that the fly ash be continuously melted and poured within critical temperature and pour rate tolerances. For example, fly ash typically melts and pours at around 2765 degrees Fahrenheit. However, at this temperature the fly ash is a gummy mass, whereas at 2875 degrees Fahrenheit the fly ash flows like water. Moreover, the diameter of the resultant fibrous strains is highly dependent upon the temperature of the molten fly ash. Accordingly, it is essential that any furnace used to melt fly ash for the production of mineral wool have the capacity to control the temperature of fly ash to precise tolerances, on the order of five to ten degrees centigrade, while processing large continuous volumes of fly ash--on the order of 40,000 lbs/hr for weeks at a time. However, no known prior art furnace has this degree of control over the temperature of high volume molten fly ash.
One example of a prior art attempt to utilize an electronic furnace to melt fly ash and produce mineral wool is illustrated in U.S. Pat. No. 2,817,695 issued to Hartwig. Hartwig employs three main electrodes placed 120 degrees from one another in a plane. A nozzle assembly is movably positioned along a line perpendicular to the plane of the main electrodes at the center point of the three electrodes. The nozzle assembly is cooled below oxidation temperature by coolant flowing in the nozzle assembly.
Hartwig recognizes the need to provide accurate temperature control and attempts to accomplish this control by cooling the nozzle assembly and by supplying heat to the nozzle in accordance with a temperature measurement of melted product passing through the nozzle assembly. Hartwig suggests that one way of achieving the requisite control is to apply an electrical potential between the nozzle and a selected one of the main electrodes to effect resistive heating of the melted product at the nozzle. However, except for stating that auxillary power to the nozzle is turned on after the nozzle assembly has been properly positioned, Hartwig provides no teaching of how the suggested resistive heating of the product adjacent the nozzle is to be accomplished. Instead, Hartwig concentrates on the structure of coolant passages in the nozzle assembly.
U.S. Pat. No. 3,147,328 issued to Le Clerc de Bussy discloses an electric glass making furnace which provides: three primary electrodes angularly spaced 120 degrees apart in the same plane; a first conductive disc positioned along a line perpendicular to the plane of the main electrodes and which passes through the center of the three primary electrodes, and with the first disc having a passageway through which melted glass may pour out of the vessel; a plurality of auxillary starting electrodes located above the plane of the three primary electrodes and movably positioned adjacent the opening of the passage in the first disc; and a second disc movably positioned along the above-mentioned line of the first disc to form a slot between the first and second discs, which slot is substantially on the same plane as the median plane of the primary electrodes.
In operation of the Le Clerc de Bussy device, with the second disc in a separated position, the starting electrodes are moved together three centimeters from each other adjacent the opening of the passageway in the first disc, and are electrically energized to melt glass adjacent the first disc. The glass between the starting electrodes is also heated with a blow pipe. The starting electrodes are withdrawn as the glass begins to melt and the primary electrodes are energized. When the glass adjacent the first disc is in a liquid state, the second disc is brought into position above the first disc and is also supplied with electrical energy.
According to Le Clerc de Bussy, in the course of normal operation a major part of the current in the primary electrodes travels from a primary electrode through the glass, from the glass to the two discs, and finally through the glass to another primary electrode. The electrical circuit diagram supplied with Le Clerc de Bussy shows the primary electrodes to be energized by a three-phase current source, and shows the first and second discs to be energized by single-phase current drawn from a three-phase power supply.
Le Clerc de Bussy recognizes that the hottest region in the molten glass is created between the two discs and the primary electrodes. However, the electrical and mechanical configuration of Le Clerc de Bussy does not appear to provide control of temperature adjacent the passageway which would be sufficient to provide for high volume melting of fly ash as is required in a high volume mineral wool manufacturing process. Instead, according to Le Clerc de Bussy, only a small stream of glass is pulled through the slit between the two discs and sucked through the passageway of the first, lower, disc.
Other examples of electronic furnaces are provided by U.S. Pat. Nos. 3,876,817 and 3,659,029 issued to Le Clerc de Bussy and by U.S. Pat. No. 3,983,309 issued to Faulkner et al. However, none of these additional patents appears to teach a furnace arrangement or method of operation which provides for the required amount of temperature control for large scale melting of fly ash.
It is, therefore, a primary object of the present invention to provide apparatus and methods of operation which can effectively convert large quantities of fly ash into high quality mineral wool.
In this regard, another object of the present invention is to provide apparatus and methods of operation which permit large scale conversion of fly ash into mineral wool through the use of multiphase electric current.
A further object of this first aspect of the present invention is to provide an electronic furnace and method which is capable of electronically generating a large amount of heat at a precisely controlled temperature over an exit orifice in a melting vessel in order to permit large amounts of fly ash immediately over that orifice to be raised to a precise temperature and to permit controlled flow of that fly ash through the orifice to produce large quantities of high quality mineral wool.
In the process of providing continuous large volume melting of fly ash, attention must be focused on the nozzle assembly and nozzle support assembly. Prior art nozzle assemblies are often very expensive to manufacture and difficult to replace. For example, in Hartwig the nozzle assembly comprises a cylindrical portion which ends in an inverted conically-shaped part, at the apex of which a product exit orifice is formed. Manufacture of such an assembly is accomplished by the complicated and expensive procedure of forming drawn tungsten or molybdenum. Moreover, water coolant tubes are provided adjacent the assembly to cool the tungsten or molybdenum. Corrosion of these coolant tubes during furnace operation may result in a disastrous steam explosion.
The U.S. Pat. No. 3,147,328 Le Clerc de Bussy nozzle assembly comprises a lower disc coupled to the upper end of a molybdenum rod which is provided with an axial passageway. A heat exchanger in the form of a plurality of fins or other radial projections is coupled to the rod, and a platinum member is attached to the lower end of the rod to define an exit passageway from the nozzle assembly. Again, the Le Clerc de Bussy nozzle assembly is obviously difficult and expensive to manufacture.
Although simpler nozzle assemblies are known, such as that disclosed in U.S. Pat. No. 2,276,295 issued to Ferguson, none appear to provide the ease of construction and lack of expense sought, and still establish an effective product exit orifice for a continuous pour, high volume furnace.
Accordingly, it is an object of another aspect of the present invention to provide a continuous pour furnace nozzle assembly which is inexpensive to manufacture and easy to replace.
In the manufacture of mineral wool from fly ash, it is necessary to provide not only a furnace having the capacity to control the temperature of the molten fly ash to precise tolerances and a nozzle assembly through which molten fly ash may pass, but also some form of apparatus to accumulate the resultant fibrous strands into mineral wool. However, as mentioned above, the fibrous strands are not produced alone. Instead, shot and other heavy undesirable non-fibrous material are intermixed with and often attached to the more desirable fibrous strands. In addition, the diameter of the strands, and hence their effective insulative capacity, often extend over a large range, and the accumulator apparatus desirably has the capacity to selectively choose a desired range of diameters.
Efforts have been made in the past to separate the shot and other heavy undesirable non-fibrous material from more desirable lighter fibrous strands. One such prior art method involves granulating bulk material containing shot and the like, and passing the material over a rotating screen through which a large portion of the shot and other non-fibrous portions are sifted out. In this operation, the lighter fibrous strains are rolled into small balls, pads, or pellets which are known in the industry as granulated wool. The fibrous balls, pads, or pellets, however, are not suitable for accumulating into high quality mineral wool by a "dry" process because these balls, pads, or pellets do not readily felt to each other so that the product of such a process has little or no tensile strength. When it is desired to use such granulated wool to make felted material, the granulated wool is first mixed and bonded together in water with wet paper pulp. The wet mixture is then compacted, dried, and cut.
Another prior art method illustrated in U.S. Pat. No. 2,319,666 issued to Drill, employs a shot-receiving hopper located directly under a stream of molten material. A blast assembly is located above the hopper to intersect the molten stream with a blast stream, such as a stream of steam, to convert the molten stream into mineral wool fibers and non-fibrous portions such as slugs and shot. A chamber is provided by Drill which encloses the blast assembly and hopper, and which also encloses a porous conveyer belt. A blower reportedly withdraws steam and air from the chamber through the belt and returns a selected portion thereof to the chamber through the hopper. This upward moving return steam and air from the hopper acts to prevent lighter mineral wool fibers from accumulating in the hopper along with heavier shot and undesirable material.
Accordingly, Drill represents an important development in the art of producing mineral wool. However, it is another object of the present invention to improve upon the mineral wool manufacturing apparatus and methods disclosed by Drill.
More specifically, an object of the present invention is to provide mineral wool manufacturing apparatus and methods which more effectively separate shot and the like from lighter fibrous strands.
In this regard, another object of the present invention is to provide mineral wool manufacturing apparatus and methods which selectively control the degree of separation of shot and the like from more desirous lighter fibrous strands.
Through the use of the furnace of the present invention, preferably with the nozzle assembly of the present invention, in combination with the fiber accumulation and shot separation apparatus and methods of the present invention, mineral wool having commercially suitable tensile strength and having a high percentage of highly desirable diameter fibrous strands can be produced. Since no known prior art apparatus or method has the temperature control, accumulation, and separation control of the apparatus and methods taught herein, the resultant mineral wool in and of itself is new and unique.
More specifically, it is well known in the prior art that mineral wool forms a most effective temperature insulator when consisting primarily of fibrous strands having an average diameter small enough to maximize the volume of air trapped between the fibers, and yet large enough to prevent presentation of a health hazard. Preferably, the strands have an average diameter of less than 15 microns yet greater than 3 microns. Strands having a diameter less than about 3 microns are considered a safety hazard due to their capacity to break loose into the open atmosphere and be ingested by humans, subjecting those humans to possible respiratory problems, and strands having a diameter greater than 15 microns result in a reduction in air space between strands to the point in that the insulative effect of the resultant mineral wool is materially lower.
It is, accordinly, yet another object of the present invention to provide a mineral wool product in which a high percentage by weight of the mineral wool, 70 to 80 percent, consists of fibrous strands having diameters within a range of about 3 microns to 15 microns.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.